riscv: dts: sifive: drop duplicated nodes and properties in sifive

The DTSI file defines soc node and address/size cells, so there is no
point in duplicating it in DTS file.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Tested-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Link: https://lore.kernel.org/r/20210920130248.145058-3-krzysztof.kozlowski@canonical.com